In most sawmills a cant is fed into a gang saw either top first or butt first. Chipping heads square the sides of the cant, which then is guided toward the saws by a series of upstream hold down rolls and a single pair of anvils. These anvils are positioned immediately downstream of the chipping heads, in a fixed spaced apart relationship on either side of the cant. The fixed anvils, the chipping heads and the saws are positioned for optimal board recovery from the cant according to instructions from an optimizer. Due to the fixed positioning of the anvils, the chipping head can not be positioned into the cant which results in excessive amounts of chipping when cants are fed butt first or for example when they have flares or bulges along their length.
The fixed anvils are spaced apart to provide a minimal clearance for through-passage of the cant. However, when asymmetric chipping loading occurs on one side of cant, for example when the chipping knives impact a side of the cant where more chipping is required, this loading results in the cant being moved laterally toward the opposite anvil. Further, the upstream hold down rolls are generally closely linearly spaced along the feed line of the cant. When a cant has traveled downstream past the last hold down roll it will be supported only by the fixed anvils. Asymmetric chipping loads may cause the cant to deflect laterally away from the optimizer's optimized board recovery solution.